Known photodetecting devices include a semiconductor substrate including a first principal surface and a second principal surface that oppose each other (see, for example, Patent Literature 1). The photodetecting device described in Patent Literature 1 includes a plurality of avalanche photodiodes operating in Geiger mode and through-electrodes electrically connected to the corresponding avalanche photodiodes. The plurality of avalanche photodiodes are two-dimensionally arranged on the semiconductor substrate. Each avalanche photodiode includes a light receiving region disposed at the first principal surface side of the semiconductor substrate. The through-electrode is disposed in a through-hole penetrating through the semiconductor substrate in the thickness direction.